README.md

930. Binary Subarrays With Sum

Given a binary array nums and an integer goal, return the number of non-empty subarrays with a sum goal.

A subarray is a contiguous part of the array.

Example 1:

Input: nums = [1,0,1,0,1], goal = 2
Output: 4
Explanation: The 4 subarrays are bolded and underlined below:
[1,0,1,0,1]
[1,0,1,0,1]
[1,0,1,0,1]
[1,0,1,0,1]

Example 2:

Input: nums = [0,0,0,0,0], goal = 0
Output: 15

Constraints:

• 1 <= nums.length <= 3 * 104
• nums[i] is either 0 or 1.
• 0 <= goal <= nums.length

Solutions (Rust)

1. Solution

use std::collections::HashMap;

impl Solution {
    pub fn num_subarrays_with_sum(nums: Vec<i32>, goal: i32) -> i32 {
        let mut count = HashMap::new();
        let mut sum = 0;
        let mut ret = 0;
        count.insert(0, 1);

        for num in nums {
            sum += num;
            ret += count.get(&(sum - goal)).unwrap_or(&0);
            *count.entry(sum).or_insert(0) += 1;
        }

        ret
    }
}